扬子陆块北缘大洪山地区莲沱组底部凝灰岩锆石U-Pb定年及其地层学意义  

Zircon U-Pb age and stratigraphic significance of the tuff from the lowermost Liantuo Formation in the Dahongshan area of the northern Yangtze Block

作　　者：宁括步 邓奇 崔晓庄 汪正江 任光明 杨青雄 NING Kuobu;DENG Qi;CUI Xiaozhuang;WANG Zhengjiang;REN Guangming;YANG Qingxiong(Chengdu Center,China Geological Survey(Geosciences Innovation Center of Southwest China),Chengdu 610218,Sichuan,China;Key Laboratory for Sedimentary Basin and Oil and Gas Resources,Ministry of Natural Resources,Chengdu 610218,Sichuan,China;Hubei Geological Survey,Wuhan 430034,Hubei,China)

机构地区：[1]中国地质调查局成都地质调查中心(西南地质科技创新中心),四川成都610218 [2]自然资源部沉积盆地与油气资源重点实验室,四川成都610218 [3]湖北省地质调查院,湖北武汉430034

出　　处：《地质通报》2024年第2期363-375,共13页Geological Bulletin of China

基　　金：中国地质调查局项目《扬子西缘俯冲增生杂岩带专项地质调查》(编号:DD20230208);四川省自然科学基金项目《四川南江-旺苍地区火地垭群沉积-变质事件及成矿地质背景研究》(批准号:2023NSFSC0275);四川省科技厅中央引导地方发展专项《扬子西缘新元古代—古生代转换期的盆地动力学及其成烃成储响应研究》(批准号:2023ZYD0153);国家自然科学基金项目《扬子北缘中元古代神农架群和打鼓石群的沉积序列、构造属性及对比研究》(批准号:41772115)。

摘　　要：扬子陆块北缘莲沱组是华南新元古代的重要地层单元之一,但其沉积时限、区域对比关系、沉积环境与沉积期古地理存在诸多争论。对大洪山地区莲沱组底部的凝灰岩进行了LA-ICP-MS锆石U-Pb定年,获得凝灰岩样品的形成年龄为798.4±4.5 Ma(MSWD=0.40,n=13)。结合前人研究成果,将莲沱组的沉积时限限定为800~714 Ma,区域上可与板溪群及其相当地层中上部、休宁组、澄江组、开建桥组、武当群和随县群进行对比,为“晋宁造山运动”不整合面之上、南华冰期之下的一套裂谷充填产物,代表了裂谷盆地全面打开,沉积范围快速扩大的充填序列,其主体为冲积扇、河流及滨浅海沉积。莲沱沉积时期,扬子陆块北缘形成了一个向北逐渐变深的裂谷盆地,此时大洪山地区的莲沱组为围绕鄂北古隆起分布的冲积扇沉积,向北则变为以随县群为代表的滨浅海—半深海沉积。The Liantuo Formation,exposed on the northern Yangtze Block,is one of the important Neoproterozoic stratigraphic units in South China.However,no consensus has been reached on its depositional period,regional correlation,depositional environment and paleogeographic characteristics so far.In this study,we obtained a zircon LA-ICP-MS U-Pb age of 798.4±4.5 Ma(MSWD=0.40,n=13)for the tuff layer from the bottom of the Liantuo Formation in the Dahongshan area.Integrating the previous reported data,the depositional period of the Liantuo Formation was constrained to ca.800–714 Ma.Regionally,the Liantuo Formation is comparable to the middle-upper part of the Banxi Group and its equivalent strata,as well as to the Xiuning Formation,Chengjiang Formation,Kaijianqiao Formation,Wudang Group and Suixian Group.The Liantuo Formation is a set of rift filling deposition,which rests on the Jinning orogeny unconformity and underlies the Nanhua Glacial Period deposition,representing a filling sequence while the rift basin fully opening and the depositional area rapidly expansion.The depositional sequence is mainly composed of alluvial fan,fluvial and littoral-neritic facies sediments.During the Liantuo Period,the northern Yangtze Block was a rift basin,which gradually deepened to the north.Meanwhile,the Liantuo Formation in the Dahongshan area represents an alluvial fan deposition that distributed around the Northern Hubei Paleo-uplift,and evolves to the littoral-neritic-bathyal deposition that represented by the Suixian Group.

关 键 词：扬子陆块北缘 莲沱组 凝灰岩 锆石U-PB定年 新元古代 地质调查工程 

分 类 号：P588.211[天文地球—岩石学] P597.3[天文地球—地质学]